New technology designed for high pressure low flow applications

Victoria, Minnesota water treatment facility needed a new pump to feed sodium hypochlorite under high pressure into the post-chlorination cycle of their water treatment process. Their previous diaphragm metering pump had serious issues with off-gassing, resulting in vapor locking that shut down the pump. After replacing the diaphragm pump with new peristaltic metering pump technology specifically designed for high pressure applications, they have significantly reduced downtime. At the same time, the pump’s fluid recovery features means they can avoid any potential chemical spills when changing out the line.

Seeking reliable and safe chemical metering pumps

The City of Victoria, MN, population around 8,800, is located in Carver County, about 30 minutes outside Minneapolis. The city provides residents with drinking water from three groundwater wells. About a decade ago, they built a water treatment facility to treat iron and manganese present in the water. They use several chemicals in the water filtration, clarification, and distribution process, including fluoride, sodium hypochlorite, polyphosphate, and sodium permanganate.

The diaphragm pump used to meter sodium hypochlorite at the post-chlorination stage was experiencing severe issues related to off-gassing. This is a common problem with diaphragm pumps metering sodium hypochlorite, according to Clark Corbett, sales engineer for Vessco, Inc., the city’s chemical feed equipment supplier. Vessco represents 60 different companies in the water and wastewater industry, and is headquartered just a few minutes’ drive from Victoria.

“Their original diaphragm pump was losing prime, off-gassing to the point that bubbles were getting into the diaphragm and vapor locking it so the pump stopped working.”

According to Corbett, there were very limited options that could deal with the application, which runs at relatively low flows (2-3 gallons per hour) – but very high pressures (90-95 pounds per square inch (psi) on discharge). He pointed the water treatment works to a brand new technology, the Qdos 20 peristaltic metering pump made by Watson-Marlow Fluid Technology Group.

Peristaltic pumps have no valves, seals or glands in the fluid path so are not affected by air entrainment or abrasive and corrosive fluids such as those found in water treatment. Importantly, the Qdos pump is made with a tube material specifically formulated for high pressure sodium hypochlorite applications.

The Qdos 20 was not even on the market when he suggested it, but Corbett was able to get a demonstration model to the site to give it a try. Victoria had already been using other members of the Qdos pump family for most of their chemical metering. Their success and familiarity with the technology made them comfortable with trying the new Qdos 20 model, which seemed to arrive on the scene just in time to solve their high pressure sodium hypochlorite application issue.

They had first tried a Qdos 30 model on polyphosphate, which is often the easiest chemical to pump. Their original diaphragm pump was situated high in the air and the suction line dipped. This caused them to lose prime quite a bit. Recalls Corbett, “When they switched to the Qdos 30 they were extremely happy, because it pulled a better vacuum, resulting in higher suction on the line, so it can stay primed the whole time.” Qdos flow rates remain constant irrespective of fluid viscosity or pressure in the application.

Since that first Qdos 30 was installed five years ago, Victoria has gradually been switching over from diaphragm pumps. They now use the Qdos 30 pump for the pre-chlorination sodium hypochlorite application, because this is a lower pressure application. They also use a Qdos 30 for metering fluoride.

Victoria ran the Qdos 20 trial model for more than a year – only replacing the ReNu pumphead once in that time. Running at between 70 and 100 psi and controlled by a 4-20mA input signal, the Qdos 20 pump significantly reduced maintenance downtime. They are currently in the process of replacing the trial model with a production unit.

According to the water plant operator Brady Lee, “We like these pumps a lot. Maintenance is fast and simple and controlling the pumps to increase flow as water demands change is very straightforward.”

Chris Miller, District Sales Manager for Watson-Marlow, who supplied the trial model, was extremely pleased with the trial success. He notes that the new technology is especially good for applications at well sites at many smaller plants, where operators are often injecting into water lines at higher pressure.

Closer look at new pump

The new pump has been designed to optimize its performance life for sodium hypochlorite applications up to 100 psi at flow rates from 0.001-5.3 gallons per hour (gph).The pumphead provides accurate, linear and repeatable low pulse flow under varying process conditions. Process uptime is maximized with no gas-locking, no valve blocking, and rapid no-tools pumphead replacement. Flow control is 5330:1 with ±1 percent accuracy. The pump offers manual, analog or contact mode functionality and has an intuitive display. Its high suction lift ensures self-priming.

The design inherently reduces maintenance. For example, the contained ReNu pumphead integrates leak detection. In the event of a tube failure, operators just quickly and safely replace one component, the pumphead, without the need for tools of special skills, and they can quickly get back to pumping.

Corbett explains, “Water applications need a reliable feed for chemicals, and it is especially important to keep sodium hypochlorite running. The Qdos 20 addressed the needs of small towns to have more flexibility. Smaller towns tend to have limited maintenance personnel. With this technology, they only need to replace the pumphhead, a relatively inexpensive part.”

Another feature Victoria likes is that they do not require any ancillaries to install or run the Qdos pumps, like pulsation dampening and back pressure valves. In addition, the fluid recovery feature allows them to run the pump in reverse to empty the line. This means they can change out the line without spilling any chemical left in the tubing, an important safety feature.

Watson-Marlow’s Chris Miller agrees. He notes that the sodium hypochlorite used for this water treatment application is extremely corrosive; the fumes will corrode anything but plastic. With the Qdos 20, any leak is contained. There is no dripping, leaking, or splashing that might get into operators’ eyes. A built in leak detector shuts off the pump to protect it in the event of any type of failure.

The consumable pumphead contains the fluid after failure and is a throwaway item. It takes only a few seconds to change, and then the plant can be back up and running. “You only need to change the pumphead about once a year, and you are good to go,” says Miller. “It’s a low price component.”

Future applications

When the new model is commercially available, Victoria is considering obtaining a second Qdos 20 pump for the pre-chlorination sodium hypochlorite application and moving the Qdos 30 they are currently using to another spot in the plant. They are also considering replacing the diaphragm pump being used to meter permanganate with another Qdos 30. The goal is to use the Qdos technology for all chemical metering pumps at some point in the future.

Miller sums it up this way. “Like so many facilities, Victoria’s maintenance staff is spread thin, so this type of cost effective and easy installation and maintenance is just what they are looking for.”